Ultra high frequency oscillator



Nov. 9, 1948. l. M; BRUNTIL ETA L 2,453,489

ULTRA KIGH FREQUENCY OSCILLATOR Filed Aug. 12, 1944 Figl.

Invent ors:

Ln u a w m n h i r T 6 0 E t M M .m .w Mm IE WT Patentecl Nov. 9,1948

OFFICE ULTRA IHGH FREQUENCY OSCILLATOR Irwin M. Bruntil, Bridgeport, and Earl F. Reillman, Fairfield, Conn, assignors to General Electric Company, a corporation of New York Application August 12, 1944, Serial No. 549,262

Claims. (Cl. 250-36) Our invention relates to electric wave generators and particularly to high frequency electronic oscillators of the tuned gridplate transmission line type.

It is a general object of our invention toprovide a new and improved high frequency oscillator.

It is a further object of our invention to provide a new and improved oscillator having a tank circuit of the grid-plate transmission line type characterized by unusually low surge impedance and low radiationlosses.

It is another object of our invention to provide, in a grid-plate transmission line oscillator, newand novel means for varying the efiective electrical length of the lineto control the oscillator frequency. a

It is still another object of our invention to provide a grid-plate transmission line tank circuit for a high frequency oscillator having high capacity per unit length and low inductance and resistance thereby to providelow'surgeimpedance and a narrow band width.

A high frequency oscillator constructed in accordance with our invention comprises a tank circuit formed of a pair of sheets of electrically conductingmaterial disposed in parallel spaced relation and having awidth great in proportion to their length in the direction of wave propag ation. Betweenproximate ends of the electrical conducting sheets remote from the grid and plate electrodes we connect a variable condenser arranged to constitute an apparent short circuit at selectable points along the line in the region of its remote end. The conducting sheets are bent transversely of the direction of wave propagation toform a pair of similar surfaces nested one within the other and having an axis of symmetry parallel to the direction of wave propagation. The outer sheet is connected to the grid electrode and the inner sheet to the plate or anode of an electron discharge device, so that the transmission line acts as a resonant circuit to feed back energy from the plate to the grid in regenerative phase, thereby to set up oscillations in the discharge device at a frequency determined by the effective electrical length of the line to the point of apparent short circuit. The total transmission line length to the point of connection of the variable condenser is approximately a quar ter wavelength or an odd multiple thereof at the desired frequency, the exact effective length being determined by the capacitance of the condenser. I

Our invention will be more fully understood and its objects and advantages'further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Figs, 1, 2, and 3 are front, rear, and side elevations, respectively, of an electron discharge device and high frequency tank circuit therefor constructed in accordance with our invention; Fig. l is a schematic perspective circuit diagramo-f a high frequency oscillator embodying ourinvention; and Fig. 5 is a simplified schematic circuit diagram of the oscillator circuit shown at Fig. l. Referring now to the drawing, we have shown an oscillator comprising anelectron discharge device l of the triode typeenclosed in a substantially cylindrical evacuated envelope and mounted upon a panel or base 2 of suitable insulating material. Theelectron discharge device I includes an anode3, a cathode 4, agrid or control electrode 5, and a cathode heating element 6. The anode 3 is provided at spacedpoints with a pair of external leads in the form of wires l and 8 extending radially outward from the cylindrical envelope. Spaced points on the grid 5 are provided with external leads in the form of a pair of radially extending wires 9 and It. An external lead wire H is connected to the cathode l and additional external lead wires 12 and H are connected to the cathode heating elcmentfi. The wires 'l-l3, inclusive, each extend radially from the substantially cylindricalevacuated envelope in substantially the same plane and provide means for mounting the discharge device l uponthe panel 2. For this purpose the panel 2 islprovided with aplurality of clip type terminal connectors Mil], inclusive, radially spaced about acircular aperture 2' in the panel 2. .The grid and anode terminal connectors ill-ll areconnectedto a plurality of studs 2l 4, respectively, which extend through the panel 2 for connection to an external tank circuit on the rear side of the panel.

At the rear side of the panel 2 are disposed-a pair of thin sheets 25 and. 26 of electrically con ducting material disposed in parallel spaced rela tion and bent into a generally U shape about an axis perpendicular to theplane of the panel 2,

so that the sheet 25 partially encloses the sheet 26. The sheets 25 and 26 may be made of copper, or other suitable metal plated with silver, copper or gold. The U-shaped sheets 25 and 26 are mechanicallymounted upon and electrically connected tothe grid and platestuds 23, Ell. and 2 l, 22, respectively. The connection of the plates 25 and 26 to the studs 23, 24 and 2!, 22, respecmote from the electrode connecting studs 2| 24 a pair of'variable condensers 2i and;28. The condensers Z-l' and 28 are mounted upon a common shaft having an insulating section 30 and are symmetrically connected between adjacent points of the parallel U-shaped plates 25;. and25 at the ends remote from the panel 2.

The condensers 21 and 28..each.comprisea plurality of alternate fixed and movable semicircular plates. The movable plates of bothcondensers. are mounted upon the shaft 2 9,and theshaft 29- is journaled at its ends in a U-shaped bracket 3|. The fixed plates of each condenser are mounted upon a pair of, electrical conducting pins 32; and 53; rigidly mounted upon. the bracket 3! and; extending longitudinallyof. the shaft 29. Each pair of supportin pins 32-, 33 iscarried by arr-insulating member 3 lwhich isconnected to the U shaped bracket 31 at opposite ends of the shaft 29 by bolts 35. As clearly shown at Fig. 2;, the electrical conducting pins 32 supporting the stationary, plates of the condensers are connected to the extremities of opposite legs of the U-shaped anode conductor Zliandthe movable plates, of each condenser are connected, to the proximate extremities of the legsof-the U-shaped g rid conductor 25-.

Thecompleteoscillator shown at Fig. a comprises. also a tubular conductor 3.6 for grounding the, cathode 4 at a low potential. point and suitablemeans for connecting the anode 3 to the positive. terminal of; a source ofunidirectional current supply, suchas a battery 37.. The tubular conductor. 36 is of such length that it forms, together with th'ecathode lead wire. II, a lineof approximately one-half wave length. at the operating frequency. This arrangement is desirable. at the high frequencies. herein contemplated in order to ensure-that. the. cathode 4 itself is at ground potential. If a cathode lead of length other, than a, half wave length or an integral multiple, thereof is. used athigh frequency, the impedance of thecathode lead itself would be sufficient to raise the cathode above ground potential.

The cathode heater leads l9 and 20 are con.- nected to a source 3.8,, of direct current or low frequency alternating current. This. connection is conveniently made by connecting the, tubular conductor in series Withthe heater, lead 25 and passing. the heater lead l5 concentrically through the conductor 36. This also shields. the heater lead from the high frequency field, preventing R. F. from appearing, on the heater.

The power supply for the oscillator is derived from the positive terminal of the battery 31 through a radio frequency choke coil 39,, a resistor 45, and a low pass filter comprising an inductance 4i and a condenser 42. Suitable grid bias is obtained through a grid leak resistor 43' connected between the grid end of the line conductor 25 and ground.

The operationof our high frequency oscillator and the effect of our new and novel tank circuit design may now be understood by referring par ticularly to Figs. 4 and 5. At Fig. 5, we have illustrated schematically the oscillator shown at Figgl. In the latter figure the grid-plate transmission line comprising the electric conducting sheets 25 and 26 has been shown as a pair of conductors 25' and 26' disposed in parallel spaced relation. The length I of the conductors 25 and 26 corresponds to the length l of the U-shaped grid and plate conducting sheets 25 and 26 between their points of connection to the electrode studs 21-24, inclusive, and their opposite ends connected; to the condensers, 21; and 28. The condensers?! .and 28 of. Fig, 4 are represented by a single variable condenser 2'! at Fig. 5. At Fig. 5 we have also shown lumped circuit constants representing certain electrode and lead capacitance and inductance between the grid and plate electrodes; of the discharge device I and the transmission lineplates 25 and 26. Specifically,

a capacitor 44-. at Fig. 5 represents the interelectrQdQgrid-to-plate.capacitance of the discharge device I and the capacitance between the external grid and plate lead wires, terminal connectors and studs. The inductances 45 and 46 of Fig. 5.represent the, inductance of the internal and. external lead wires, terminal connectors, and connecting studs for' the gridand plate, respectively. Since the inherent impedances 4,4, 45, and 45 necessarily formapart ofthe grid-plate transmission line. andareof appreciable value at the frequencies under consideration, they must. be taken into account in designing. the tank circuit comprising theconducting. plates 25. and 26.

Thetotal. electrical; length of the transmission line between the, electrode 3. and 51 of the dis? charge device I andtheremote. ends of the conducting sh'eetslf-i and. 261s, determined by the umpedcir uit constants 4,4, 45, and stand the dis ribu edinductan e and capac an o h length-l oi the conductors 25 and 2,6 themselves, This length is approximately an oddmultiple of a, quarter wave length at thefrequency of the desired oscillations. By an odd multiple of a quarter wave length we intend to include a single quarter wavelength, andin the drawingwe have l ustr ed'ia ine t ucii e t he v iable capacitor of B 5 ssufi ciently l r e so at at its. maximum value itoifers substantially no impe a e.i qf i r nt nf e. e i ed i frequency andtherefore constitutes substantially a short circuit across .the remote. ends of the transmission line. Whenfiiiiusted to lesser values/of capacitance, the condenser 27. no longer constitutes a short circuit but oifers an appreciable impedance less than the characteristic imped; ance of the transmission line.

It is understood by those slrilled in the art that a short-circuits d' transrnission lineofthe type described above possesses a characteristic or resonant frequency determined by its effective electrical length. At this frequency standing waves will appearon the linein such phase relation that the line possesses. the characteristics off'a parallel resonant circuit. The e fective electrical-length of, the line is thatv length between the anode andfgrid electrodes 3 and sand the pointershort-circuiting at the remote endof, the line. we have found that the oint, of. a parent short; circuit between the conductors, 2.5, and 2,6 of- Fi-g. 5* maybe varied by variation of thecaa a c of? h cr d ser .1-. Similarl he point of apparent, short circuit between. the sheets 2'5 and2$ of Figs. I 1-4 may be Vari bat e condensers. 2-? and 28, This is. i1lustrated,graphi,.-' ral at E gh '9. h ..dQ fi T Q 4i. r pr n s. a tandin ave i. volta ehavina a maxi-v mum value at theopen; end, or" the line between the anode and grid electrodes 3 and 5 andazero alue at mint. P loc ledhetweenth nds f the transmission line conductors 25 and 26C, The location'ofthe point P and, therefore, the length andfrequency of the generated waves may be varied by varying the capacitance of. thecom denser 21 .and thus changing the impedance between the conductors 25' and 26 at the points of connection of the condenser 21. When the condenser 21 has its maximum capacitance, its

impedance, as previously stated, is substantially lish between the remotej ends of the conductors, 25 and 26' and across the condenser 27 a voltage determinedlby the impedance of the condenser In a practical embodiment of our invention de signed to generate oscillations having a wave length of the order of 40 centimeters, it was found that the major portion of thequarter wave length transmission line was constituted by the inherent lumped circuit constants 44, S5, and 46; so that thelength i of the external line constituted by the parallel conducting plates and 26 was approximately only two and one-half centimeters.

From the foregoing detailed explanation of the construction, arrangement, and operation of our invention, it will be observed that we have incorported into a simple, compact, and inexpensive structure a number of new and novel features which add greatly to the efficiency of operation of a high frequency electric wave generator of the type herein described. Heretofore, it has been proposed to vary the effective length of an oscillator tank circuit formed of parallel conducting sheets by providingthe sheets with interfitting sliding sections arrangedto change the actual physical length of the sheets. This arrangement is awkward, mechanically complicated, and extremely susceptible to maladjustment. In accordance with our invention, we have found that by forming the external transmission line of conducting sheets having a width great relative to their length, it is possible to so decrease the line surge impedance by increase in line capacity that the effective electrical length of the line may be varied by connecting across its remote ends a variable condenser of practical size. rangement of the parallel conducting sheets in U or equivalent symmetrical shapes with the plate conductor substantially enclosed by the grid conductor. By this arrangement the plate conductor is shielded, so that power loss by plate radiation is appreciably diminished and the percentage band width of the line decreased. Also, by shaping the transmission line conductors symmetrically in a plane transverse to the direction of wave propagation along the line and utilizing an electron discharge device having a pair of external leads from each of the grid and plate Further advantage is derived from our arthe art and therefore weuwish tohave it under stood that we intend inthe appended claims to cover all such modifications as fall withinthe rue spirit and scope of our invention. f

What we claim as new and desire Letters Patent'of the United States, is: a 1

1. A high frequency wave generatorincluding anelectron discharge device having an i anode, a cathode and a control electrode, a tank circuit including a transmission line formedsofwa pair of sheetsof electrically conducting material disposed in parallel spaced relation, one'end of one of said sheets being connected to said anode and one end of the other of said. sheets being connected to said control electrode; said sheets having a width great relative to their length and being curved in a plane transverse to the direction of wave propagation; said length being measured in said direction. from oneof saidends oi oneof said sheets to" the respectively opposite end thereof, thesheet connected to said control electrodeysurrounding and shielding the sheet connected to said anode. i 1 2. A high frequency wave generator including an electron discharge device having an anode,

a cathode and a control electrode disposedin an evacuated envelope, said discharge device includingexternal anode and controlelectrod conductors in substantially the sameplane,a tank circuit including a pair ofsimilarly curved metal sheets nested one within the other and having a plane of symmetry substantially perpendicular to the plane of said conductors, the length of said sheets in a direction perpendicular to said plane of said conductorsbeing sufficient to provide an odd multiple of a quarter wavetransmission line between opposite ends of said line at the frequency of said waves, said anode being connected to said one sheet at one end of said line and said control electrode being connected to said other sheet at said one end.

3. A high frequency wave generator comprising an electron discharge device having an anode, a cathode and a control electrode, a transmission line tank circuit comprising a pair of metallic sheets disposed in' parallel spaced relation and connected at proximate near ends to said anode and control electrode respectively, said sheets being curved transversely of the length as determined by the direction of wave propagation so that the sheetconnected to said control electrode at leastpartially surrounds the sheet connected to said anode, the length of said transmissionline between opposite ends of said sheets being approximately an odd multiple of a quarter wave length at the frequency of said. waves,

and a variablecondenser connected between the electrodes symmetrically connected to opposite sides of the transmission line conductors, the potential distribution upon the plate and grid of the tube is rendered more uniform. In this way unbalance within the tube is largely avoided and the efiect of inductance and capacitance in the electrode leads is minimized.

While we have described only a preferred embodiment of our invention by way of illustration, many modifications will occur to those skilled in proximatefar ends of said sheets remote from said anode and control electrode, said length being measured from said near ends to said far ends.

4. A high frequency wave generator comprisfing a substantially planar supporting base, an electron discharge device having an anode, a

cathode and a control electrode disposed ina substantially cylindrical evacuated envelope, said anode and control electrode being each provided with a pair of external lead wires extending radially from said discharge device in substantially the plane of said base, a plurality of terminal connectors mounted upon said base for supporting engagement with said external lead wires, a tank circuit comprising a pair of nested substantially U-shaped metal sheets mounted upon said base and directly connected to said to secure b 7, terminal connectors, said U-shaped sheets having: an axis of symmetry substantially perpendicular to the: plane of said base, the outer sheet being connected at the edge adjacent said base-to said pair of control electrode leads at symmetrical points on opposite sides of said axis of symmetry and the. inner sheet being similarly connected to said pair of anode leads, said sheets being of such length in the direction of said axis of symmetry that the total electrical length of said transmission line is approximately a quarter wave length at the frequency of said-waves, and a pair of variable condensers connected between said metal sheets atsymmetrical' points on opposite sides of 'said. axis of symmetry and at the edge remote from said base. 7 v

5. A high frequency wave generator including an electron discharge device having an anode, a cathode and a control electrode, a transmission line tank circuit comprising a pair of similar nested metallic sheets connected atone end of said line to said anode and control electrode respectively and having an axis of symmetryin thedirection of wavepropagation, said-direction being from said one end: to the opposite end of said line, the outer sheet having symmetrically disposed points on opposite side of said axis of symmetry connected to said control electrode,

8 the-inner sheet having similar points con-- nected to said: anode, and a pair of variable condens'ers connected between said sheets at'symmetrical. points on opposite sides of said: axis of symmetry and at the opposite end of said line.

' IRWIN M. BRUNTIL.

EARL F. REIHMANL REFERENCES CITED Theiollowingreferences are of record in the file of this patent:

UNITED STATES 667,751 France Dec. 18,1929

Certificate of Correction Patent N 0. 2,453,489. November 9, 1948.

IRWIN M. BRUNTIL ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 27, claim 5, for the word side read sides;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 29th day of March, A. D. 1949.

THOMAS F. MURPHY,

Assistant (lommz'ssioner of Patents. 

